Microelectronic devices commonly have bump bond structures with tin-containing solder on copper pillars to provide connections to lead frames, chip carriers, and such. During operation of the microelectronic devices, current densities of 103 amps/cm2 to 105 amps/cm2 through the bump bond structures may lead to device failures. At these current densities, electromigration combined with ohmic heating in the copper pillar bump bond structures facilitate atomic diffusion of copper into the solder to form copper-tin intermetallic compounds (IMCs) such as Cu6Sn5 and Cu3Sn. Formation of the IMCs involves volume shrinkage, leading to formation of voids. Voids may accumulate in the bump bond structures, resulting in device failures.
One common practice is to use a barrier metallurgy (such as Ni) to inhibit copper diffusion leading to void initiation and growth. Using a barrier metallurgy slows down the dissolution of the copper into the solder joint but does not stop it completely. Electromigration failures may occur at a later stage.